核融合炉用複合超電導体の安定性に対する14MeV中性子照射効果

抄録

The neutron irradiation effects on cryostability of composite superconductors for fusion reactor are studied based on Maddock's condition. In particular, to estimate the effects of 14MeV neutrons we assumed that the irradiation-induced degradation of critical temperature, critical current density and conductivity of stabilizer are determined by the damage energy depending on the neutron energy spectrum. The cryostability is found to decrease sensitively with increasing the fraction α of fusion neutrons with energy of 10-14MeV to the total neutrons;
(1) The Cu/superconductor ratio R_ns, to stabilize the conductor, must be increased remarkably with increasing α as well as the total dose of the neutron fluence. The optimized R_ns has a maximum value of about 80 in case of Nb₃Sn with transition temperature T_c=15K, critical current density J_c=10⁵A/cm₂ and stabilizer resistivity ρ=5×10^-8Ωcm. The fluence to give the maximum R_ns shifts to the lower one with increasing α. In order that the composite conductor is fully stabilized under the irradiation (<10¹⁸n/cm²), one must choose the larger R_ns than the maximum one.
(2) For the small R_ns (-4), the stabilized overall current density decreases by several ten percents even at the fluence where T_c and J_c change only a few percent. This effect is dominated by the severe increase of ρ.